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The Windows operating system allows you to run many programs at the same time. If you run a program, it will store a lot of data in memory. This can be graphics and other things. For example, if you run a browser, and you have 10 tabs open, each tab, with all the graphics, will be stored in memory.

Your computer has memory, also known as RAM. But if you look at the total sum of all programs open and how much RAM they actually need, you will find out that it requires far more RAM than your system actually has. For example, you can be running Windows 10 on a system with 8 GB, run Chrome with 20 tabs open, Chrome alone may use somewhere between 2 and 4 GB. Windows itself can also use up to 4GB.

Then you have your drivers installed, run some other programs, maybe a game even, and before you know it, you will be consuming 16GB to 24GB of RAM, and you only have 8GB. So how is this possible, you may ask?

Well, this is where the Page File comes in. Windows will try and keep the most relevant data in active memory and stores all programs that you currently are not using into the pagefile to free up memory.

Since Windows 10, this process has been changed though. Windows will first attempt to compress the memory and only if it cannot compress it any further, it will start swapping out data to the pagefile.

The reason is that a pagefile does many reads/writes and if this is located on a slow disk, then a pc becomes significantly slower the more memory is consumed. Also with SSD's to reduce wear on the SSD, this technique was created by Microsoft.

In Windows 10, you will want to set the pagefile to be managed by Windows though, this will ensure that the compression works best. Keep in mind that if the system drive is used for a pagefile and the other disks aren't, and your system drive runs out of space, windows will start to complain with errors such as written by you. So make sure you have at least 10% of your harddisk space free on C. 25% would be recommended though.